Conventionally, in a vehicle such as an automobile, a front seat, e.g., the driver's seat or passenger seat, is provided with a side airbag device for protecting an occupant from impact applied laterally relative to the body of the vehicle. The side airbag device comprises an igniter, inflator, side airbag, impact detection sensor, etc., and is secured to, for example, the frame of a seatback.
If impact is applied to, for example, a door member (an example of a lateral portion of the vehicle body) that closes a lateral door opening for the passenger seat, the impact detection sensor detects this impact. Then, the igniter is actuated so that gas is emitted from the inflator. The side airbag is inflated by a pressure of the gas emitted from the inflator.
The inflated side airbag projects outward from the seatback to be located between the occupant and door member. The side airbag is large enough to cover that region of the occupant which is oriented in the vehicle width direction. The region of the occupant which is oriented outward in the vehicle width direction mainly covers the range from the chest region to the lumbar region.
Since the side airbag is thus located between the occupant and the lateral portion of the vehicle body, impact applied laterally relative to the vehicle body can be absorbed by the inflated side airbag.
On the other hand, an arm of the occupant in the seat is normally located beside the chest region. In other words, the arm and chest region of the occupant are arranged side by side in the vehicle width direction. If the side airbag is inflated in this state, the arm of the occupant will be located between the inflated side airbag and the chest region of the occupant.
While the impact applied to the lateral portion of the vehicle body is absorbed as the side airbag is inflated, the side airbag subjected to the impact moves inward in the vehicle width direction. When this is done, the arm of the occupant is pressed against the chest region. If the arm is pressed against the chest region as the side airbag moves inward in the vehicle width direction, impact applied to the chest region of the occupant may sometimes increase.
In order to keep the arm from being pressed against the chest region due to deployment of the side airbag, therefore, a structure has been proposed in which a seam is provided at that part of the side airbag which faces the arm of the occupant, thereby suppressing inflation of that part of the side airbag which faces the arm. As the inflation of that part of the side airbag which faces the arm is suppressed, the arm can be kept from being pressed against the chest region (see Patent Document 1, for example).
In order to bind the occupant in a balanced way, a structure has been proposed in which a non-inflation portion is formed at that part of the side airbag which faces the arm of the occupant, and that part of the side airbag which corresponds to the shoulder of the occupant is inflated (see Patent Document 2, for example).